Screw propeller



March 29, 1932. o. HERMANSON SCREW PROP ELLER F iled May 19 192a Fig.2.

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Patented Mar. 29, 1932 OSCAR HERMANSQN, or nn'wyonx, N. v.

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Application filed ma 19,

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If a propeller driving somevehicle travels at a rate of a hundred miles an hour, it advances 146,66 feet per second, and if the screw makes 1200 revolutions 7 per minute, or 20 revolutions per second, the'pitch, that is the length, measured alon the axis, of a complete turn of the thread 0 the screw, must be at l least'7l333 feet'or 88 inches, if the screw shall not impede the motion. At this speed the propeller will merely revolve without striking the air, and if it shall have a pro pelling effect, the speed of the revolving screw must be increased until it overcomes the resistance of the air. Taking, for example, a

":1," 6 foot propeller with a hub of 4 inches diameter and 5 inches high, the single bladeof the propeller, at a pitch of 88 inches, will constitute the 5/88=1/17.6th part of the complete screw surface, the thread of the screw around the hub will measure /ss (410 :1726 5.05 sch-es, r

and the thread of the screwat the circumference Wlll measure because the manufacturers find no material metal propeller blades, made of drop-forged steel or other alloys, have the shape of a twisted table knife, but looking at wooden propellers, we find on these only in spots true screw faces, while the whole blade represents a clumsy cudg'el whichfswinginp; around, is

El) flailing the air and causes a terrible noise in 1928.;"Srial no; 279,066.11

steachof a propelling ellect'fi This accounts for the stupendous waste of power on airplanes,- andbecause it is lack of'rigidity inthe material'that so far has defeatedthexc'orre ct shape of propellersplshallaltogether'dispen'se with that rigidity and. shall relybnly on'the tensile strength of theimaterialin m propeller.

l Building a light but-geometrically-correctscrew of such material-i of high tensile strength, this screw may he pliable orinaybe stiifpbutits shape'will' be maintained while it revolves by tl iecentrifugal forceof some weight which I insert at the peripheral edge a I I r p I of tlte'blade. *j v 7 ln'the foregoing example of a6 foot propeller, that makes 20 revolutions per-second, the material in the: peripheral edge of the blade revolves'with a v'eloc'ityof 1201 376 .99 1: feet per second, butthe centrifugal force of 7 a weight IV revolving with the velocity in a circle with radius?" is Wcflgr, ,9 being the acceleration by gravity or 32,2 feet per second:

Therefore thepullofa weight of W pounds revolving with the velocity of" 377; feet p51" second in a' circle" of feet radius, is 37 I 32,2 '3 147'11315W' pounds; This' fmea ns' every poundat'the periphe'ral rim ofthe'pro f pellerfpullswithla centrifugalforceof'over 1471; pounds when the pro ell'er travels with '0 aspeed-ef 100 iles per our at the lowest number-of 20 'revolutions per second, when the propeller'd'oesno workat all. But m p derto'maintainthat speed 'of lfOO miles per:

hour, we vmust increase the number ofrevolu s5 tions' and at 1800 revolutions per minute, or 30 revolutions per second,-because the pull isinproportion to the square of thevelocity 1:;

the centrifugahforce becomes 9 /{lff2;2"5 timeseater 01 331046 pounds for'every p'ound m Elie"periphei'a'l rim. 1

*Wh'ile this'shows the reason why no 'satis factory screw can be shaped of" wood or other material of: similar strengthfilt atth e same time shows thatapliablescrew can be h up of band iron or of ribbonsof steel of h tensile strength that will be stretched by centrifugal force in revolving, when we reinforce" V the'peripheral rim of these-rev: with butafevv; l V poundsof weightjReinforcing the 1379mm V V peripheral rim of the afore defined propeller blade with 14: inches of a one half inch rod of lead, which weighs 1.1215 pounds, this will cause a pull of 3712.85 pounds at 1800 revolutions per minute, and if the blade is built up of 14 steel ribbons, each one inch wide, this will give only 265 pounds for each ribbon. But such ribbons of steel will easily hold 50 tons to the square inch, that is to say, they need be no thicker than one three hundredth of an inch.

I11 Fig. 1 a 6 foot propeller is shown the two blades of which are built up, each of seven two inch wide ribbons, with a hub 1 of 4 inches diameter and 5 inches high. At the periphery the blades are loaded Witha inch rod of lead 2, 14 inches long and weighing 1.1215 pounds, exerting a pull of 8712.85 pounds at 1800 revolutions'per minute. In Fig. 2 a single ribbon is shown with two holes 3 at its peripheral end, that is slung aroundthe leaden bar and riveted. Fig. 3 shows the manner in which the blade is attached to a wooden hub. Of course,such blades may be attached to the hub in manyother ways, and any desired number of blades'may be attached to the hub in the same manner. In Fig. 3 the 7 overlapping ribbons that form'the blade are shown with their central ends bent at a right angle at the line a-b in Fig. 2 and pressed to the hub 1 by a bar 4.- that is tied by wires 5 to the hub 1. In Fig. 4 an angle bar 6 is shown to press the blade, to the planed face of the hub. This angle bar 6 is shown to be held by three screw bolts so thatthe slots 9 allow to revolve it around the fixed center bolt 8 and in this manner to change the pitch of the screw. 7 a

When revolving, the ribbons will be strongly pressed against one another by centrifugal force and. by the pressure of the air, so that no air will escape between them, which also might be prevented by agglutinating adjacent ribbons by means of any adhesive orelastic material, like rubber. Y

Instead of building up each blade of many single ribbons, as afore described, I may also build a blade of a single sheet by properly folding it. Fig. 6 shows a single rectangular sheet which is to be cut at the dot and dash lines 10 and is to be bent on one side along the six parallel lines 11, and on the other side along the six dotted lines 12. When folded along these lines, the sheet forms the fan Fig. 5. \Vith 14: holes punched at the bottom of the sheet Fig. 6, the rim will be folded around the rod 13 and riveted, as shown in Fig; 5, while the other end of the folded fan is bent at a right angle and with a bar and seven 2 wires tied to the hub in the manner afore described. V V

In case the ribbons in Fig. 1 are not stiff enough to hold the blades stretchedin place when at rest, I reinforce the blades with light but rigid bars-14, just strong enough to hold by centrifugal force.

2. A propeller as claimed in claim 1 wherein the central end of each ribbon is fastened to an angle bar that is attached to the hub by means of screws passing through slots in the angle bar whereby the pitch of theblades may be adjusted. .7 OSCAR HERMANSON. 1 

